Triplet-state spin labels for highly sensitive pulsed dipolar spectroscopy

ABSTRACT

Pulsed dipolar spectroscopic methods allow nanometer distance measurements between pairs of spin labels. We have proposed a new spin labelling approach, based on the population of a chromophore triplet under light excitation, testing it on a peptide-based spectroscopic ruler and a photosynthetic protein. We have applied a modified Pulsed Electron DOuble Resonance (PELDOR) sequence where the photogeneration of the triplet spin precedes the conventional 4-pulse PELDOR sequence. In this experiment, the triplet-state serves as detection spin while the stable nitroxide is the pump spin. Alternatively, a new method, Laser-Induced Magnetic Dipole spectroscopy (LaserIMD), has been proposed: the nitroxide signal is detected while a time varying laser pulse acts as a pump to generate the triplet state [C. Hintze, D. Bücker, S. Domingo Köhler, G. Jeschke and M. Drescher, J. Phys. Chem. Lett. 7 (12), 2204 (2016)]. For the first time, in this work, we compare the two dipolar techniques performing X-band experiments in the same experimental conditions and deriving analytical expressions for the echo modulation by the density matrix formalism.

GRAPHICAL ABSTRACT

KEYWORDS:

• PELDOR
• DEER
• LaserIMD
• triplet state
• spin label

Acknowledgments

The authors thank all collaborators involved in the realisation of the work reviewed in this contribution and whose names are given in the corresponding references.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support from the University of Padova [PRAT2014–CPDA145097/14] is gratefully acknowledged.